Let's see.. would be great to actually win some money from some of those gambling machines.
But if you mean, Christmas wish from MAME*dev*, that's a different story.
Votrax SC-01 sound chip emulation for games like Q*bert and Wizard of Wor, but also the few Apple II Mockingboard games that used it (as if RB's Apple II driver and OG's 6502 core improvements need more awesome sauce).
Qsound emulation
Integration of MAMEhooker force-feedback support directly into MAME in a cross-platform way (you didn't say we had to be realistic, did you?)
Tighter coupling of MAME and MESS (though a lot of great work this year to that end)
Improved psx driver support - though extremely cool that Mednafen and no$psx are doing it this year.
An auto-threading build of MAME/MESS, whenever that falls out of Microsoft's orbit.
A DECO cassette dump of Manhattan, so I could gift it to gregf.